Shell and tube falling film heat exchangers have an array of tubes extending between and through two spaced apart tube sheets surrounded by a shell. The shell is provided with an inlet and an outlet so that a suitable heat exchange liquid or gas can be circulated through the shell to cool or heat a liquid flowing through each tube.
Each end of the array of tubes can be left open, or exposed, for use in some processing operations. For other operations, one or both ends can be enclosed by a liquid retaining header, which may or may not have a removable cover or access port.
Although shell and tube heat exchangers are generally used to heat a liquid feed stream, they can be used for cooling such a stream. Shell and tube heat exchangers of the described types can be used as freeze exchangers for producing fresh water from brackish water and seawater, for concentrating fruit and vegetable juices, and industrial crystallization processes. As the liquid flows through each tube, it can be cooled enough to crystallize a solid from the liquid. Thus, by cooling seawater, ice is obtained which when separated, washed and melted provides potable water. When a fruit or vegetable juice is similarly chilled, ice forms and is removed to provide a concentrated juice.
Freeze exchangers of the described type can use any cooling fluid on the shell side to cool a liquid flowing downwardly through the tubes. The fluid can be fed through one end and removed through the other end of the freeze exchanger in a substantially unidirectional flow. Some suitable cooling fluids are refrigerant gases such as ammonia and Freon brand refrigerants.
Whether the heat exchanger is used to heat or cool a process liquid, it is desirable to be able to control the thickness and uniformity of the falling film in each tube. Generally, acceptable results are not obtained by simply supplying enough liquid to flow down such tube because the feed to each tube is most often nonuniform, with some tubes receiving much more, and others much less, liquid than desired for optimum heat exchange results. There is a need, accordingly, for apparatus which will facilitate supplying the process liquid to the tubes to produce falling films uniformly thick and evenly distributed on the internal surface of each tube.